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The Cemento-Dentino-Canal Junction, the Apical Foramen, and the Apical Constriction: Evaluation by Optical Microscopy
JOURNAL OF ENDODONTICS Copyright © 2003 by The American Association of Endodontists
Printed in U.S.A. VOL. 29, NO. 3, MARCH 2003
The Cemento-Dentino-Canal Junction, the Apical Foramen, and the Apical Constriction: Evaluation by Optical Microscopy Elı´as Harra´n Ponce, DDS, and Jose´ Antonio Vilar Ferna´ndez, BA, PhD
The CDC junction is the point where the cementum meets the dentinal canal, the cemental cone extending from here (2). Kuttler (2) observed that the base of the cemental cone is ⫻524 m in young people, 18 to 25 age group, and ⫻659 m in people over 55 yr old. Another anatomic region to consider is the AC. The blood vessels at this level are narrower, making the resolution of inflammatory episodes within the root canal more difficult. From a biological point of view, the AC is an extremely important point to consider when terminating the preparation of the root canal, because the existence of functional blood flow controls the inflammatory process (3). The invasion of this point, in an apical direction, with instrumentation and/or filling material could affect apical healing. A previous study (4) on 90 anterior teeth demonstrated that the average diameter of the root canal at the AC was 425 m, 369 m, and 375 m for central incisors, lateral incisors, and cuspids, respectively. The final important anatomic reference is the AF. It has been observed (2, 5) that its diameter varies between 500 and 1500 m and it is located, in most cases, to one side of the apical vertex (6). Knowledge of the anatomy and histological composition of the apical third of the tooth in determining the ideal apical limit for instrumentation and filling of the root canal is of vital importance. Hence, the aim of this study was to determine histologically the localization of the CDC junction and the diameters of the AF and root canal at the CDC junction.
The cemento-dentino-canal junction, the apical constriction, and the apical foramen are the principal reference points used to determine the apical limit for instrumentation and root canal filling. For a better understanding of these structures, the objective of this study was to evaluate histologically the localization of the cemento-dentino-canal junction and the diameters of the apical foramen and root canal at the cemento-dentino-canal junction. Eighteen anterior maxillary teeth (canines, central, and lateral incisors) were used, from which 269 histological sections were obtained and evaluated by optical microscopy. The results indicated that the longest extension of the cementum into the root canal was observed in the canines, this value decreasing in the lateral incisors, and even more so in the central incisors. The widest diameter of the apical foramen corresponded to the lateral incisors, followed by the canines and the central incisors. The diameter of the root canal at the cemento-dentino-canal junction was greatest in the canines and lowest in the central and lateral incisors. Great variability was observed in the measurements of the extension of the cementum into the root canal. AQ: 1
MATERIALS AND METHODS For this study 18 anterior teeth of the maxillary (7 canines, 5 lateral incisors, 6 central incisors) were used. The patients were selected randomly, and the average age was 42 yr old. Clinically speaking, the teeth had to have pulpal vitality, to be without periodontal or periapical disease, without root reabsorption, and have been in normal occlusion. Once the extractions were performed, the different sides of the roots were marked for each tooth. Later these were separated from the crown at the middle third of the root and prepared for their fixation in 10% neutral-buffered formalin solution. After 48 h, decalcification was achieved with formic acid-sodium citrate solution. Before their inclusion in paraffin, the side where the AF emerged was visualized by means of a stereoscopic magnifying
The ideal root canal filling is one which is performed threedimensionally and that completely obliterates the area from the root canal to the cemento-dentino-canal (CDC) junction. Proper sealing of the root canal at this level makes it impossible for bacteria, and their toxins, to invade the periapical tissues and to feed from the nutritive material contained in these (1). This objective may be achieved if pulpal extirpation and instrumentation are carried out to the CDC junction or its surroundings. To determine this “ideal apical limit” the main anatomic and histological references to consider are the CDC junction, the apical foramen (AF), and the apical constriction (AC). 214
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FIG 1. Areas evaluated: AF (1); extension of the cementum (2 and 3) and diameter of the root canal at the CDC junction (4).
glass (Citoval 2; Carlzeiss, Germany). This allowed the roots to be oriented in such a way that the longitudinal histological sections, serial and of 6-m thickness, contained the entire root canal. The histological sections were stained with hematoxylin and eosin and Gomori trichrome, evaluated by optical microscopy, and the measurements were obtained by means of an EWF10⫻ wide field micrometric ocular lens (ZUZI, Nikon, Japan).
Areas Being Evaluated and Criteria for Data Collection The teeth used were those that allowed at least 10 histological sections of the entire root canal. A total of 269 histological sections were analyzed. Observation by optical microscopy showed that the apical third of the tooth was divided by the root canal into two sides, right and left, called “Side A” and “Side B,” respectively, for their analysis (Fig. 1). Data collection was achieved from the following areas (Fig. 1): 1. Localization of the AF; 2. Extension of the cementum into the root canal at sides A and B; 3. Diameter of the AF; 4. Diameter of the root canal at the CDC junction. Measurements of the extension of the cementum on each side (A and B) of the histological section were made from the outermost part or edge of the foramen to where its extension was the greatest in the root canal (CDC junction). The diameter of the AF was measured from the most extreme points of the same, as indicated in the definition of AF of Kuttler (2). Lastly, the diameter of the root canal was measured at the point where the greatest extension of the cementum into the root canal was observed. Statistically and based on the different normality tests (Kolmogorov and Shapiro-Wilks), it was concluded that the different measurements taken were not distributed evenly. Due to the lack of homogeneity, a nonparametric test was used, specifically contrasting the Wilcoxon signed rank test (paired data) to compare the distributions.
FIG 2. Right upper lateral incisor. Different extensions of the cementum into the root canal (arrows) and the AF at one side of the apical vertex (V) are observed. Hematoxylin-eosin stain. Original magnification ⫻ 10.
RESULTS Localization of the AF When considering the localization of the AF in the 18 cases evaluated, 3 cases (16.6%) showed its presence on the mesial side (Fig. 2), 8 cases (44.4%) on the distal side, 2 cases (11.1%) on the palatial side, and finally 5 cases (27.7%) on the apical vertex (Figs. 3 and 4). Extension of the Cementum into the Root Canal Data were collected to investigate the extension of the cementum into the root canal. The average extension length observed for both sides and in a total of 269 histological sections (therefore, a total of 538 samples to study) was ⫻834.29 m (⫾33.55). Then, a statistical comparison of the extension of the cementum on side A versus side B was performed for each tooth individually and jointly, depending on the type of tooth. 1. Each tooth individually: individual analysis of each tooth revealed great variability in the measurements obtained for both sides. In some cases, the Wilcoxon test concluded that the extension was
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FIG 3. Right upper central incisor. AF in coincidence with the apical vertex. The extension of the cementum on side “B” is ⫻ 303.8 m and on side “A” ⫻ 616 m (arrows). Observe an area of dentin on side “A” in opposition to the area of cementum on side “B”(d). Hematoxylin-eosin stain. Original magnification ⫻ 10.
Journal of Endodontics
FIG 4. Right upper canine. Significant extension of the cementum into the root canal, side “A” being ⫻ 2132.54 m (arrows) and side “B” ⫻ 1546.8 m (arrows). Foramen at the apical vertex (V). Gomori trichrome stain. Original magnification ⫻ 10.
significantly greater (p ⬍ 0.05) on side A, and in others, the greatest extension was present on side B. Fig. 5 describes the measurements recorded for both sides of a particular tooth. 2. By type of tooth: joint analysis of the data according to the type of tooth showed that in all types of teeth, the average extension of the cementum was longer on side B. This finding was deduced from the joint representation of the 99% confidence intervals for mean values with respect to the type of tooth and side appearing in Fig. 6. Conclusions from Table 1 and Fig. 6: 1. The greatest extension of the cementum was observed in canines (1009.44 m on side A and 1395.74 m on side B), decreasing in lateral incisors and being further reduced in central incisors. Application of several Wilcoxon tests showed that these differences were statistically significant (p ⬍ 0.05). 2. With the incisors, especially with the central ones, the observations were quite homogeneous. However, variability of the data was notable with the canines: standard deviation for the canines was 80.51 for side A and 128.18 for side B, whereas the central incisors were 17.76 and 19.85, respectively.
FIG 5. Graph of the extension of the cementum in the right upper lateral incisor from Fig. 2; Side “B” ⫻ 592.5 m (⫾ 110.90) and side “A” ⫻ 427.5 m (⫾ 90.97). Observe the variations in the extension of the cementum for the same tooth.
Diameter of the AF The diameter of the AF for the different types of teeth investigated was ⫻453.63 m (⫾21.85) for canines (Fig. 4), ⫻519.21 m (⫾31.49) for lateral incisors (Fig. 2), and ⫻353.98 m for central incisors (⫾18.79) (Fig. 3) (Table 2). The measurements
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FIG 6. Graph of the 99% confidence interval corresponding to the different types of teeth evaluated. TABLE 1. Statistical analysis of the extension of cementum on side A and side B for the samples studied Area
Tooth
No. of sample
Mean
Median
Standard error
A
C LI CI
97 89 83
1000.44 642.02 344.00
600.00 378.00 350.00
80.51 54.64 17.76
B
C LI CI
97 89 83
1395.74 978.48 515.28
740.00 840.00 550.00
128.18 45.82 19.85
C ⫽ Canine; LI ⫽ lateral incisor; CI ⫽ central incisor.
TABLE 2. Statistical analysis of the diameters of the apical foramen and root canal at the CDC junction for the samples studied Area
Tooth
No. of sample
Mean
Median
Standard error
D
C LI CI
97 89 83
353.20 292.25 298.16
325.00 275.00 280.00
17.83 13.32 12.87
F
C LI CI
97 89 83
453.63 519.21 353.98
407.00 560.00 350.00
21.85 31.49 18.79
F ⫽ Diameter of the apical foramen; D ⫽ diameter of the root canal at the CDC junction; C ⫽ canine; LI ⫽ lateral incisor; CI ⫽ central incisor.
obtained for each tooth were not homogeneous, demonstrating the irregular shape of the foramen. Diameter of the Root Canal at the CDC Junction The diameter of the root canal at the CDC junction was ⫻353.20 m (⫾17.83) for canines (Fig. 4), ⫻292.25 m (⫾13.32) for lateral incisors (Fig. 2), and ⫻298.16 m (⫾12.87) for central incisors (Fig. 3) (Table 2). As with the AF, the lack of homogeneity in the measurements for each tooth showed the irregularity of the canal at this level. The Wilcoxon signed rank test was also used to determine whether the diameter of the AF and the diameter of the root canal at the CDC junction had the same median. Once again the test
revealed a difference that was statistically significant (p ⬍ 0.05), thus, demonstrating that the diameter measurements tend to be different at both anatomic points. The joint analysis of the data according to the type of tooth reveals that the observations at the AF and the diameter of the root canal are rather homogeneous, causing little deviation in the data. DISCUSSION The cemental canal, the AF, and the AC are the principal anatomic reference points for determining the apical limit for instrumentation and filling of the root canal. Kuttler (2), when analyzing the localization of the CDC junction on the basis of the length of the extension of the cementum into the
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root canal, demonstrated that the length of the cemental canal in people between 18 and 25 yr old was ⫻508 m and ⫻343 m on the right and left sides, respectively, of the histological sections. In people over 55, these values were ⫻802 m and ⫻619 m for the right and left sides, respectively. Another study (7), determined the extension of the cementum as being between 110 m and 1016 m. However, if the study of Kuttler (2) is performed on different types of teeth it would not reveal the different extensions of the cementum that each tooth could have, given only one section was made per tooth. In the present study, serial histological sections demonstrate that the analysis of each individual tooth differs from the results of the analysis by type of tooth and of the global analysis of the teeth evaluated. In the analysis of each individual tooth, the extensions of the cementum differ from one cut to another, displaying values that vary between 200 m and 800 m (Fig. 5). When the data are grouped by type of tooth, successive Wilcoxon tests showed that the differences were statistically significant (p ⬍ 0.05). When our data are analyzed in general (538 measurements), a mean of 834.29 m (⫾33.55) was obtained, this value differing from those obtained previously. This last way of analyzing the data was used in previous studies (2–7). In our observations we have been able to prove that when the root canal terminated to one side of the root, the extension lengths of the cementum were never the same, even when their terminations coincided. We have observed that in these cases, generally speaking, the concave side of the curve presented the greatest extension of the cementum at the root. The great variability of the extension of the cementum in the same tooth and in different types of teeth demonstrates that the CDC junction should be considered just as a point at which two histological tissues meet inside the root canal. Clinical localization is impossible and so is trying to complete instrumentation in this area, and filling it would be utopia. The AF has been defined by Kuttler (8) as the circumference or rounded edge, like one of a funnel or crater, that differentiates the termination of the cemental canal from the exterior surface of the root. For the author mentioned, the diameter of the foramen in people in the age range 18 to 25 was ⫻502 m, and in those over 55 it was ⫻681 m, demonstrating its growth with age. For Green (9), the diameter of the foramen varied between 30 m and 2000 m with an average of 570 m. In another study (10) performed on anterior teeth, the average diameter of the foramen in upper teeth was 297 m and in lower teeth 260 m. Our observations, with the average age being 42 yr, show values that are within the range reported for previous studies (8 –10), the greatest diameter being that of lateral incisors (⫻519.21 m; ⫾31.49) and the smallest of central incisors (⫻353.98 m; ⫾18.79) (Table 2). The localization of the AF in the root has been the focus of analysis for different authors. Burch and Hulen (11) reported that in 92.4% of teeth studied, the major foramen opened short of the anatomic apex and that the distance between the foramen and anatomic root apex was 590 m. Gutierrez and Aguayo (12) observed that the foramen openings never coincided with the principal axial axis of the root, always opening before the apical vertex at a distance between 200 and 3800 m. For Green (9) 50% of the foramens coincided with the apical vertex, whereas those that did not were found at an eccentric position 2 mm away. In our study, in 27.7% of the cases the foramen was located at the apical vertex, running along its main axis. The highest percentage, 44.4%, was observed at the distal side of the root. The reference point most used by the clinician to set the apical limit for instrumentation and filling is the AC. Kuttler (8) observed in patients, in the age range 18 to 25, that when the CDC junction
Journal of Endodontics
was located at the same level, only in 53% of the cases did it coincide with the AC. Its diameter was ⫻306 m. In patients over 55 yr old this coincidence was observed in 60%, and the diameter was ⫻274 m. In our study, sides A and B were found at the same level in only 5% of the cases. In another previous study (4), the average labiolingual diameters of the canals at the AC of central incisors, lateral incisors, and canines were 425 m, 369 m, and 375 m, respectively. In our study, the average diameter of the root canal, on the side showing the greatest extension of the cementum was ⫻353.20 m for canines, ⫻292.25 m for lateral incisors, and ⫻298.16 m for central incisors. The measurements were taken at the level where the cementum reached farthest into the canal, because our criteria for placing the instrumentation and filling it is to avoid damaging or invading the root cementum, tissue that plays a major role in posttreatment scarring after endodontic procedures. When comparing the diameter of the foramen with that of the AC, our results coincide with those of previous studies (2– 6), reporting the possible conical shape of the cemental canal. It is important to be aware that in this type of work, where evaluations are based on measurements, there are altering variables, such as age of the individuals (2), the different shapes of the foramen contour (5), the presence of inflammatory processes (13), the influences of occlusion, pressure, mesial displacement (14), and the methodology used for their analysis, which can mask or modify the results. We coincide with other authors (15, 16) in that the application of the foramen and AC as a reference point for determining where to stop apically should be used with much caution. Our results allow us to conclude that: (a) the CDC junction is simply the point at which two histological tissues converge inside the root canal, susceptible to modification depending on each particular clinical situation and on the varying extensions of the cementum into the root canal; (b) the AC and the AF are not reliable anatomic references used to set the apical limit in preparations. Their use as a reference or apical stopping point can result in the production of lesions in the apical and periapical tissues. The authors thank Ana Ma Eiroa for the translation of this work. Dr. Ponce is in private practice in La Corun˜ a, Spain. Dr. Vilar Ferna´ ndez is professor, Computer Sciences Department, University of La Corun˜ a, La Corun˜ a, Spain. Address requests for reprints to Elı´as Harra´n Ponce, Donantes de Sangre 2- 1° A, 15004 La Corun˜a, Espan˜a.
References 1. Grove C. Why root canals should be filled to the dentinocemental junction. J Am Dent Assoc 1930;17:293– 6. 2. Kuttler Y. Microscopic investigation of root apexes. J Am Dent Assoc 1955;50:544 –52. 3. Cohen S, Burns RC. Vı´as de la pulpa. 7th ed. Espan˜a: Harcourt, 1999: 209. 4. Mizutani T, Ohno N, Nakamura H. Anatomical study of the root apex in the maxillary anterior teeth. J Endodon 1992;18:344 –7. 5. Green D. A stereomicroscopic study of the root apices of 400 maxillary and mandibular anterior teeth. Oral Surg 1956;9:1224 –32. 6. Pineda F, Kuttler Y. Mesiodistal and buccolingual roentgenographic investigation of 7,275 root canals. Oral Surg 1972;33:101–10. 7. Guttuso AM, Seidberg BH, Langeland K. Apical root anatomy of human maxillary central incisors. Oral Surg 1976;5:694 –9. 8. Kuttler J. Fundamentos de endo-metaendodoncia pra´ctica. 2nd ed. Mexico: Mendez Otero, 1980:8. 9. Green D. A stereo– binocular microscopic study of the root apices and surrounding areas of 100 mandibular molars: preliminary study. Oral Surg Oral Med Oral Pathol 1955;8:1298 –304. 10. Chapman CE. A microscopic study of the apical region of human anterior teeth. J Br Endod Soc 1969;3:52– 8.
Vol. 29, No. 3, March 2003 11. Burch IG, Hulen S. The relationship of the apical foramen to the anatomic apex of the tooth root. Oral Surg 1972;34:262– 8. 12. Gutierrez JH, Aguayo P. Apical foraminal openings in human teeth. Number and location. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 1995;79:769 –77. 13. Walton R, Torabinejad M. Endodoncia, principios y pra´ ctica clı´nica. Me´ xico: Interamericana McGraw-Hill, 1991:27.
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14. Meyer W. Ist das foramen apical stationar? Deutsche Monatschr Zahneilk 1927;45:1016 –21. 15. Dummer PM, McGinn JH, Rees DG. The position and topography of the apical canal constriction and apical foramen. Int Endod J 1984;17:192– 8. 16. Kobayashi C, Suda H. A basic study on the electronic root canal length measurement. Part 4. A comparison of 6 apex locators. Jpn J Conserv Dent 1993;36:185–92.
Printed in U.S.A. VOL. 29, NO. 3, MARCH 2003
The Cemento-Dentino-Canal Junction, the Apical Foramen, and the Apical Constriction: Evaluation by Optical Microscopy Elı´as Harra´n Ponce, DDS, and Jose´ Antonio Vilar Ferna´ndez, BA, PhD
The CDC junction is the point where the cementum meets the dentinal canal, the cemental cone extending from here (2). Kuttler (2) observed that the base of the cemental cone is ⫻524 m in young people, 18 to 25 age group, and ⫻659 m in people over 55 yr old. Another anatomic region to consider is the AC. The blood vessels at this level are narrower, making the resolution of inflammatory episodes within the root canal more difficult. From a biological point of view, the AC is an extremely important point to consider when terminating the preparation of the root canal, because the existence of functional blood flow controls the inflammatory process (3). The invasion of this point, in an apical direction, with instrumentation and/or filling material could affect apical healing. A previous study (4) on 90 anterior teeth demonstrated that the average diameter of the root canal at the AC was 425 m, 369 m, and 375 m for central incisors, lateral incisors, and cuspids, respectively. The final important anatomic reference is the AF. It has been observed (2, 5) that its diameter varies between 500 and 1500 m and it is located, in most cases, to one side of the apical vertex (6). Knowledge of the anatomy and histological composition of the apical third of the tooth in determining the ideal apical limit for instrumentation and filling of the root canal is of vital importance. Hence, the aim of this study was to determine histologically the localization of the CDC junction and the diameters of the AF and root canal at the CDC junction.
The cemento-dentino-canal junction, the apical constriction, and the apical foramen are the principal reference points used to determine the apical limit for instrumentation and root canal filling. For a better understanding of these structures, the objective of this study was to evaluate histologically the localization of the cemento-dentino-canal junction and the diameters of the apical foramen and root canal at the cemento-dentino-canal junction. Eighteen anterior maxillary teeth (canines, central, and lateral incisors) were used, from which 269 histological sections were obtained and evaluated by optical microscopy. The results indicated that the longest extension of the cementum into the root canal was observed in the canines, this value decreasing in the lateral incisors, and even more so in the central incisors. The widest diameter of the apical foramen corresponded to the lateral incisors, followed by the canines and the central incisors. The diameter of the root canal at the cemento-dentino-canal junction was greatest in the canines and lowest in the central and lateral incisors. Great variability was observed in the measurements of the extension of the cementum into the root canal. AQ: 1
MATERIALS AND METHODS For this study 18 anterior teeth of the maxillary (7 canines, 5 lateral incisors, 6 central incisors) were used. The patients were selected randomly, and the average age was 42 yr old. Clinically speaking, the teeth had to have pulpal vitality, to be without periodontal or periapical disease, without root reabsorption, and have been in normal occlusion. Once the extractions were performed, the different sides of the roots were marked for each tooth. Later these were separated from the crown at the middle third of the root and prepared for their fixation in 10% neutral-buffered formalin solution. After 48 h, decalcification was achieved with formic acid-sodium citrate solution. Before their inclusion in paraffin, the side where the AF emerged was visualized by means of a stereoscopic magnifying
The ideal root canal filling is one which is performed threedimensionally and that completely obliterates the area from the root canal to the cemento-dentino-canal (CDC) junction. Proper sealing of the root canal at this level makes it impossible for bacteria, and their toxins, to invade the periapical tissues and to feed from the nutritive material contained in these (1). This objective may be achieved if pulpal extirpation and instrumentation are carried out to the CDC junction or its surroundings. To determine this “ideal apical limit” the main anatomic and histological references to consider are the CDC junction, the apical foramen (AF), and the apical constriction (AC). 214
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FIG 1. Areas evaluated: AF (1); extension of the cementum (2 and 3) and diameter of the root canal at the CDC junction (4).
glass (Citoval 2; Carlzeiss, Germany). This allowed the roots to be oriented in such a way that the longitudinal histological sections, serial and of 6-m thickness, contained the entire root canal. The histological sections were stained with hematoxylin and eosin and Gomori trichrome, evaluated by optical microscopy, and the measurements were obtained by means of an EWF10⫻ wide field micrometric ocular lens (ZUZI, Nikon, Japan).
Areas Being Evaluated and Criteria for Data Collection The teeth used were those that allowed at least 10 histological sections of the entire root canal. A total of 269 histological sections were analyzed. Observation by optical microscopy showed that the apical third of the tooth was divided by the root canal into two sides, right and left, called “Side A” and “Side B,” respectively, for their analysis (Fig. 1). Data collection was achieved from the following areas (Fig. 1): 1. Localization of the AF; 2. Extension of the cementum into the root canal at sides A and B; 3. Diameter of the AF; 4. Diameter of the root canal at the CDC junction. Measurements of the extension of the cementum on each side (A and B) of the histological section were made from the outermost part or edge of the foramen to where its extension was the greatest in the root canal (CDC junction). The diameter of the AF was measured from the most extreme points of the same, as indicated in the definition of AF of Kuttler (2). Lastly, the diameter of the root canal was measured at the point where the greatest extension of the cementum into the root canal was observed. Statistically and based on the different normality tests (Kolmogorov and Shapiro-Wilks), it was concluded that the different measurements taken were not distributed evenly. Due to the lack of homogeneity, a nonparametric test was used, specifically contrasting the Wilcoxon signed rank test (paired data) to compare the distributions.
FIG 2. Right upper lateral incisor. Different extensions of the cementum into the root canal (arrows) and the AF at one side of the apical vertex (V) are observed. Hematoxylin-eosin stain. Original magnification ⫻ 10.
RESULTS Localization of the AF When considering the localization of the AF in the 18 cases evaluated, 3 cases (16.6%) showed its presence on the mesial side (Fig. 2), 8 cases (44.4%) on the distal side, 2 cases (11.1%) on the palatial side, and finally 5 cases (27.7%) on the apical vertex (Figs. 3 and 4). Extension of the Cementum into the Root Canal Data were collected to investigate the extension of the cementum into the root canal. The average extension length observed for both sides and in a total of 269 histological sections (therefore, a total of 538 samples to study) was ⫻834.29 m (⫾33.55). Then, a statistical comparison of the extension of the cementum on side A versus side B was performed for each tooth individually and jointly, depending on the type of tooth. 1. Each tooth individually: individual analysis of each tooth revealed great variability in the measurements obtained for both sides. In some cases, the Wilcoxon test concluded that the extension was
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FIG 3. Right upper central incisor. AF in coincidence with the apical vertex. The extension of the cementum on side “B” is ⫻ 303.8 m and on side “A” ⫻ 616 m (arrows). Observe an area of dentin on side “A” in opposition to the area of cementum on side “B”(d). Hematoxylin-eosin stain. Original magnification ⫻ 10.
Journal of Endodontics
FIG 4. Right upper canine. Significant extension of the cementum into the root canal, side “A” being ⫻ 2132.54 m (arrows) and side “B” ⫻ 1546.8 m (arrows). Foramen at the apical vertex (V). Gomori trichrome stain. Original magnification ⫻ 10.
significantly greater (p ⬍ 0.05) on side A, and in others, the greatest extension was present on side B. Fig. 5 describes the measurements recorded for both sides of a particular tooth. 2. By type of tooth: joint analysis of the data according to the type of tooth showed that in all types of teeth, the average extension of the cementum was longer on side B. This finding was deduced from the joint representation of the 99% confidence intervals for mean values with respect to the type of tooth and side appearing in Fig. 6. Conclusions from Table 1 and Fig. 6: 1. The greatest extension of the cementum was observed in canines (1009.44 m on side A and 1395.74 m on side B), decreasing in lateral incisors and being further reduced in central incisors. Application of several Wilcoxon tests showed that these differences were statistically significant (p ⬍ 0.05). 2. With the incisors, especially with the central ones, the observations were quite homogeneous. However, variability of the data was notable with the canines: standard deviation for the canines was 80.51 for side A and 128.18 for side B, whereas the central incisors were 17.76 and 19.85, respectively.
FIG 5. Graph of the extension of the cementum in the right upper lateral incisor from Fig. 2; Side “B” ⫻ 592.5 m (⫾ 110.90) and side “A” ⫻ 427.5 m (⫾ 90.97). Observe the variations in the extension of the cementum for the same tooth.
Diameter of the AF The diameter of the AF for the different types of teeth investigated was ⫻453.63 m (⫾21.85) for canines (Fig. 4), ⫻519.21 m (⫾31.49) for lateral incisors (Fig. 2), and ⫻353.98 m for central incisors (⫾18.79) (Fig. 3) (Table 2). The measurements
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FIG 6. Graph of the 99% confidence interval corresponding to the different types of teeth evaluated. TABLE 1. Statistical analysis of the extension of cementum on side A and side B for the samples studied Area
Tooth
No. of sample
Mean
Median
Standard error
A
C LI CI
97 89 83
1000.44 642.02 344.00
600.00 378.00 350.00
80.51 54.64 17.76
B
C LI CI
97 89 83
1395.74 978.48 515.28
740.00 840.00 550.00
128.18 45.82 19.85
C ⫽ Canine; LI ⫽ lateral incisor; CI ⫽ central incisor.
TABLE 2. Statistical analysis of the diameters of the apical foramen and root canal at the CDC junction for the samples studied Area
Tooth
No. of sample
Mean
Median
Standard error
D
C LI CI
97 89 83
353.20 292.25 298.16
325.00 275.00 280.00
17.83 13.32 12.87
F
C LI CI
97 89 83
453.63 519.21 353.98
407.00 560.00 350.00
21.85 31.49 18.79
F ⫽ Diameter of the apical foramen; D ⫽ diameter of the root canal at the CDC junction; C ⫽ canine; LI ⫽ lateral incisor; CI ⫽ central incisor.
obtained for each tooth were not homogeneous, demonstrating the irregular shape of the foramen. Diameter of the Root Canal at the CDC Junction The diameter of the root canal at the CDC junction was ⫻353.20 m (⫾17.83) for canines (Fig. 4), ⫻292.25 m (⫾13.32) for lateral incisors (Fig. 2), and ⫻298.16 m (⫾12.87) for central incisors (Fig. 3) (Table 2). As with the AF, the lack of homogeneity in the measurements for each tooth showed the irregularity of the canal at this level. The Wilcoxon signed rank test was also used to determine whether the diameter of the AF and the diameter of the root canal at the CDC junction had the same median. Once again the test
revealed a difference that was statistically significant (p ⬍ 0.05), thus, demonstrating that the diameter measurements tend to be different at both anatomic points. The joint analysis of the data according to the type of tooth reveals that the observations at the AF and the diameter of the root canal are rather homogeneous, causing little deviation in the data. DISCUSSION The cemental canal, the AF, and the AC are the principal anatomic reference points for determining the apical limit for instrumentation and filling of the root canal. Kuttler (2), when analyzing the localization of the CDC junction on the basis of the length of the extension of the cementum into the
218
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root canal, demonstrated that the length of the cemental canal in people between 18 and 25 yr old was ⫻508 m and ⫻343 m on the right and left sides, respectively, of the histological sections. In people over 55, these values were ⫻802 m and ⫻619 m for the right and left sides, respectively. Another study (7), determined the extension of the cementum as being between 110 m and 1016 m. However, if the study of Kuttler (2) is performed on different types of teeth it would not reveal the different extensions of the cementum that each tooth could have, given only one section was made per tooth. In the present study, serial histological sections demonstrate that the analysis of each individual tooth differs from the results of the analysis by type of tooth and of the global analysis of the teeth evaluated. In the analysis of each individual tooth, the extensions of the cementum differ from one cut to another, displaying values that vary between 200 m and 800 m (Fig. 5). When the data are grouped by type of tooth, successive Wilcoxon tests showed that the differences were statistically significant (p ⬍ 0.05). When our data are analyzed in general (538 measurements), a mean of 834.29 m (⫾33.55) was obtained, this value differing from those obtained previously. This last way of analyzing the data was used in previous studies (2–7). In our observations we have been able to prove that when the root canal terminated to one side of the root, the extension lengths of the cementum were never the same, even when their terminations coincided. We have observed that in these cases, generally speaking, the concave side of the curve presented the greatest extension of the cementum at the root. The great variability of the extension of the cementum in the same tooth and in different types of teeth demonstrates that the CDC junction should be considered just as a point at which two histological tissues meet inside the root canal. Clinical localization is impossible and so is trying to complete instrumentation in this area, and filling it would be utopia. The AF has been defined by Kuttler (8) as the circumference or rounded edge, like one of a funnel or crater, that differentiates the termination of the cemental canal from the exterior surface of the root. For the author mentioned, the diameter of the foramen in people in the age range 18 to 25 was ⫻502 m, and in those over 55 it was ⫻681 m, demonstrating its growth with age. For Green (9), the diameter of the foramen varied between 30 m and 2000 m with an average of 570 m. In another study (10) performed on anterior teeth, the average diameter of the foramen in upper teeth was 297 m and in lower teeth 260 m. Our observations, with the average age being 42 yr, show values that are within the range reported for previous studies (8 –10), the greatest diameter being that of lateral incisors (⫻519.21 m; ⫾31.49) and the smallest of central incisors (⫻353.98 m; ⫾18.79) (Table 2). The localization of the AF in the root has been the focus of analysis for different authors. Burch and Hulen (11) reported that in 92.4% of teeth studied, the major foramen opened short of the anatomic apex and that the distance between the foramen and anatomic root apex was 590 m. Gutierrez and Aguayo (12) observed that the foramen openings never coincided with the principal axial axis of the root, always opening before the apical vertex at a distance between 200 and 3800 m. For Green (9) 50% of the foramens coincided with the apical vertex, whereas those that did not were found at an eccentric position 2 mm away. In our study, in 27.7% of the cases the foramen was located at the apical vertex, running along its main axis. The highest percentage, 44.4%, was observed at the distal side of the root. The reference point most used by the clinician to set the apical limit for instrumentation and filling is the AC. Kuttler (8) observed in patients, in the age range 18 to 25, that when the CDC junction
Journal of Endodontics
was located at the same level, only in 53% of the cases did it coincide with the AC. Its diameter was ⫻306 m. In patients over 55 yr old this coincidence was observed in 60%, and the diameter was ⫻274 m. In our study, sides A and B were found at the same level in only 5% of the cases. In another previous study (4), the average labiolingual diameters of the canals at the AC of central incisors, lateral incisors, and canines were 425 m, 369 m, and 375 m, respectively. In our study, the average diameter of the root canal, on the side showing the greatest extension of the cementum was ⫻353.20 m for canines, ⫻292.25 m for lateral incisors, and ⫻298.16 m for central incisors. The measurements were taken at the level where the cementum reached farthest into the canal, because our criteria for placing the instrumentation and filling it is to avoid damaging or invading the root cementum, tissue that plays a major role in posttreatment scarring after endodontic procedures. When comparing the diameter of the foramen with that of the AC, our results coincide with those of previous studies (2– 6), reporting the possible conical shape of the cemental canal. It is important to be aware that in this type of work, where evaluations are based on measurements, there are altering variables, such as age of the individuals (2), the different shapes of the foramen contour (5), the presence of inflammatory processes (13), the influences of occlusion, pressure, mesial displacement (14), and the methodology used for their analysis, which can mask or modify the results. We coincide with other authors (15, 16) in that the application of the foramen and AC as a reference point for determining where to stop apically should be used with much caution. Our results allow us to conclude that: (a) the CDC junction is simply the point at which two histological tissues converge inside the root canal, susceptible to modification depending on each particular clinical situation and on the varying extensions of the cementum into the root canal; (b) the AC and the AF are not reliable anatomic references used to set the apical limit in preparations. Their use as a reference or apical stopping point can result in the production of lesions in the apical and periapical tissues. The authors thank Ana Ma Eiroa for the translation of this work. Dr. Ponce is in private practice in La Corun˜ a, Spain. Dr. Vilar Ferna´ ndez is professor, Computer Sciences Department, University of La Corun˜ a, La Corun˜ a, Spain. Address requests for reprints to Elı´as Harra´n Ponce, Donantes de Sangre 2- 1° A, 15004 La Corun˜a, Espan˜a.
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